This invention relates to a heat trap which prevents heat loss resulting from convection currents in water heater systems. The heat trap comprises a housing component adapted for mounting on water heater inlet and outlet ports, a mounting component rigidly supported within the housing, and at least one seal component rigidly attached to the mounting component and extending from the mounting component to the inside surface of the housing component. The seal component seals against water flow resulting from convection currents, thereby reducing energy loss from the water heater system, while permitting water flow when water is drawn from the water heater system.